The objective of the work is to discover how the development of nerve cells proceeds. The plan is to determine, at the phenomenological level, the chain of events that occur as a presumptive nerve cell becomes a fully differentiated neuron. Both in vivo and in vitro preparations of amphibian spinal neurons have already been established in this laboratory, and studied by anatomical and physiological techniques. A population of nerve cells, the Rohon-Beard neurons, have been birthdated and the development of their ultrastructure in the spinal cord has been studied. The onset and further development of electrical excitability of these cells has been examined. The development of the action potential goes through the same developmental sequence in vitro, in a large group of neurons. The project is concerned with three further aspects of the development of these nerve cells. The first is the onset and development of chemosensitivity to GABA, which depolarizes these cells. The second aspect is the development of the ability to take up (and inactivate) neurotransmitter (e.g., GABA). The third aspect is the formation of synapses on these nerve cells. Data will be obtained by intracellular recording, autoradiography, and electron microscopy, respectively.